For American idioms, I recommend these 2 books:

 

Speak English Like an American, by Amy Gillett

More Speak English Like an American, by Amy Gillett

There are a couple of good references: www.phrases.org.uk is a fairly sensible website (I've seen other sites which invent ridiculous stories for idioms), so I usually look there for some decent opinions. Idioms Organiser by Jon Wright is also quite useful, as it explains the importance of the imagery in each idiom. Hopefully you can find a copy somewhere.